Panicker Lata
Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085, India.
J Colloid Interface Sci. 2007 Jul 15;311(2):407-16. doi: 10.1016/j.jcis.2007.03.052. Epub 2007 Mar 31.
The effect of the preservative propyl paraben (PPB) on the phase transition and dynamics of dipalmitoyl phosphatidic acid (DPPA)-buffer (pH 7.4/9.3) vesicles has been studied using DSC and ((1)H and (31)P) NMR. These investigations were carried out with DPPA dispersion in both multilamellar vesicular (MLV) and unilamellar vesicular (ULV) forms. DSC results indicate that the mechanism by which PPB interact with the DPPA vesicles is similar in MLV and ULV and is independent of pH of the buffer used to form the dispersion. However, for a given concentration of PPB, the perturbation in DPPA bilayer is more when the dispersion is prepared in buffer pH 7.4. PPB affected both the thermotropic phase transition and the molecular mobility of the DPPA membrane. In the presence of PPB, the gel to liquid crystalline phase transition temperature (T(m)) of the DPPA vesicles decreases hence increases membrane fluidity due to reduced headgroup-headgroup interaction. For all concentrations, the PPB molecules seem to get intercalated between the polar groups of the phospholipids with its alkyl chain penetrating into the co-operative region. At high PPB concentration, additional transitions are observed whose intensity increases with increasing PPB concentration. The large enthalpy values obtained at high PPB concentration suggest that presence of PPB makes the DPPA bilayer more ordered (rigid). The interesting finding obtained with MLV is that the stable gel phase of DPPA-buffer (pH 9.3/7.4) system in the presence of high PPB concentration becomes a metastable gel phase, this metastable gel phase on equilibration at 25 degrees C or when cooled to -20 degrees C transforms to a stable crystalline phase(s). The intensity of this new phase(s) increases with increasing PPB concentration. However, the transition temperatures of these new phases are not significantly changed with increasing PPB concentration. The effect of inclusion of cholesterol in the PPB-free and PPB-doped DPPA dispersion was also studied.
已使用差示扫描量热法（DSC）和（（1）H 和（31）P）核磁共振（NMR）研究了防腐剂对羟基苯甲酸丙酯（PPB）对二棕榈酰磷脂酸（DPPA）-缓冲液（pH 7.4/9.3）囊泡的相变和动力学的影响。这些研究是针对以多层囊泡（MLV）和单层囊泡（ULV）形式存在的 DPPA 分散体进行的。DSC 结果表明，PPB 与 DPPA 囊泡相互作用的机制在 MLV 和 ULV 中相似，且与用于形成分散体的缓冲液的 pH 无关。然而，对于给定浓度的 PPB，当在缓冲液 pH 7.4 中制备分散体时，DPPA 双层中的扰动更大。PPB 影响了 DPPA 膜的热致相变和分子流动性。在 PPB 存在下，DPPA 囊泡的凝胶态到液晶态的转变温度（T(m)）降低，因此由于头基-头基相互作用的减少而增加了膜流动性。对于所有浓度，PPB 分子似乎插入到磷脂的极性基团之间，其烷基链穿透到协同区域。在高 PPB 浓度下，观察到额外的转变，其强度随 PPB 浓度增加而增加。在高 PPB 浓度下获得的大焓值表明，PPB 的存在使 DPPA 双层更加有序（刚性）。在 MLV 中获得的有趣发现是，在高 PPB 浓度下，DPPA-缓冲液（pH 9.3/7.）系统的稳定凝胶相变成了亚稳凝胶相，该亚稳凝胶相在 25℃平衡或冷却至-20℃时转变为稳定的结晶相。这些新相的强度随 PPB 浓度增加而增加。然而，这些新相的转变温度不会随 PPB 浓度增加而发生显著变化。还研究了在不含 PPB 和掺杂 PPB 的 DPPA 分散体中加入胆固醇的影响。
